As methods for improving slidability of polyoxymethylene resins, the following are known, namely, a method of adding esters of 1,4-butanediol with fatty acids to polyoxymethylene resins (JP-B-55-23304), a method of adding borates of glycerin monofatty acid esters (JP-B-57-15616), a method of adding polyolefins having an active hydrogen, polyethylene and isocyanates (JP-A-4-126758 or U.S. Pat. No. 5,344,875), a method of adding copolymers of .alpha.-olefins and ethylene-vinyl monomers (JP-A-49-40346), a method of adding powders of ultra-high-molecular-weight polyethylene (EP-A-148743), etc. However, according to these methods, the slidability at room temperature has been improved to some extent, but the problems of increase of friction coefficient against noncrystalline resins and increase in abrasion wear under high load and at high temperature have not been solved at all.
Furthermore, JP-A-2-66365 discloses use of a composition obtained by adding a thermoplastic elastomer and a lubricant to a polyoxymethylene resin for low-noise gears. However, this reference makes no mention of the specific lubricant as used in the present invention and the method disclosed in this reference cannot give the slidability with respect to non-crystalline resins under high load and high temperature as aimed at by the present invention. JP-A-4-36341 discloses a method of adding a thermoplastic elastomer and an adduct of alcohol with alkylene oxide to a block copolymer containing a polyacetal, but this reference makes no mention of the specific lubricant as used in the present invention and the method disclosed in this reference cannot give the slidability with respect to noncrystalline resins under high load and high temperature as aimed at by the present invention.
On the other hand, there are known a method of blending polyoxymethylene with a polyolefin (JP-B-42-19498), a method of adding a liquid ethylene-.alpha.-olefin random copolymer (JP-A-4-239566), a method of adding a modified .alpha.-olefin polymer (JP-A-59-204652), and a method of adding a polyether copolymer having an average molecular weight of at least 500 (JP-A-5-70678). However, these known compositions have made substantially no improvement of the slidability with respect to noncrystalline resins under high load and high temperature as aimed at by the present invention.
The object of the present invention is to provide a polyoxymethylene resin composition having low friction coefficient and excellent abrasion resistance against noncrystalline resins under high load and high temperature (60-100.degree. C.), particularly in point-contact reciprocation sliding test.